The present invention relates to a logic circuit and more particularly a logic circuit especially adapted to be used in VLSI systems.
ECLs (emitter-coupled logic circuits) have been recently widely used in various high-speed electronic circuits. ECLs which are fundamentally differential amplifiers can operate at high speeds and are adapted to be integrated.
When the input signals which are same in phase are applied to a prior art logic circuit, the logical outputs are indeterminate and sometimes the output signals which are opposite in phase may be derived. Therefore a multiplicity of such logic circuits are integrated into a large-scale logic circuit and if the large-scale circuit has some defects, the output signals which are opposite in phase are derived. As a result, it has been impossible to positively detect the internal defects.